This invention relates to an apparatus for producing bags, and more particularly to a machine for making, filling and sealing bags made from a continuous sheet of sealable film.
More particularly, the invention relates to an improved forming tube around which the sealable film is wrapped to form a sleeve and through which the product is dropped to fill the bag.
There are numerous types and sizes of form-fill-seal machines commercially available. These machines typically pull a sealable film from a continuous roll over a forming shoulder that wraps the film into a generally tubular shape and overlaps the longitudinal edges. As the film leaves the forming shoulder it surrounds the outer surface of a vertical hollow forming tube. The usual forming tube is machined, to precise tolerances, from stock tubular material. The outer surface is turned to insure a smooth and uniform cylindrical surface, and parallel flat elongated areas are machined on opposite sides on the tube for cooperation with advancing belts to pull the film from the roll. In addition, securing surfaces are machined to facilitate attaching spreaders and other attachments to the forming tube and for accurately mounting the forming tube in its proper location on the machine.
Form-fill-seal machines include some type of dispensing means for filling the bag with product. In a typical machine a product dispensing hopper is located above the upper end of the forming tube and functions to dispense, at the appropriate time, a measured amount of product into the interior of the forming tube.
A vertical sealing device is located adjacent the forming tube and functions to form a seam along the overlapped longitudinal edges of the sealable film to form it into a sleeve. A pair of advancing belt devices are located on opposite sides of the forming tube that cooperate with longitudinal flat surfaces on the forming tube to pull the sealable film off its roll and over the forming shoulder.
An end sealing device is located below the lower end of the forming tube that functions to form both the bottom and top lateral seals for the bags.
A cutting means is provided to sever a filled and sealed bag from the next bag that is yet to be completed.
A form-fill-seal machine can be adapted to produce a variety of different size and or shaped bags, within its range. To adapt a machine for a different size or shaped bag it is usually necessary to replace the forming tube with a different one of appropriate size and shape. A form-fill-seal machine of the type described above is described and claimed in common owned U.S. Pat. No. 3,287,199 which is incorporated herein by reference.
The forming tubes used in current machines are fabricated from relatively thick walled cylinders in order to insure the necessary structural strength after machining the flats for the advancing belts. As a result, the finished forming tube is heavy and difficult to handle and the task of changing forming tubes is difficult and time consuming. Also, as a result of the extensive machining operations required in their fabrication, they are very expensive.
In forming an acceptable bag, it is important that the advancing belts be able to pull the sealable film down smoothly and evenly to avoid wrinkling, stretching or tearing of the film. The sleeve formed from the sealable film tends to cling to the smooth cylindrical surface of conventional forming tubes requiring a relatively large force from the advancing belts to index the sleeve down the forming tube.
The interior of the forming tube, being cylindrical, facilitates swirling of the product as it falls through the interior of the forming tube. The swirling product takes a greater amount of time to settle into the bag before it can be sealed and thus slows down the filling process.
Clamps that grasp the cylindrical surface of the forming tube are used to secure the forming tube in place on the machine. Proper alignment is not inherent in such a mounting and special care must be taken before clamping the forming tube in place to insure proper positing of the advancing belt flats and attachments such as the spreaders.